answer to #3 is you can definitely cut a standard sim to micro sim size. U can buy a sim cutter of ebay for next to nothing or you could get a replacement sim for your phone.
Once it's unlocked by the carrier - it's permanently network unlocked. If it's unlocked by jailbreaking - restoring it would probably make it revert back to the original carrier.
Once you have upgraded to iOS6 - but can not downgrade. You will have to wait till a solution is found to JB iOS6. Could be weeks, could be months.